User Manual

November ’00 Chapter 5. Installation and Use

5.4 Programming a Transponder

To write data to a read/write transponder the transmitter of the RF module must be

switched off and on periodically after the power pulse is completed. As shown in Fig-

ure 14 each data bit has the same length t_bit, but the duration t_offL or t_offH during

which the transmitter is switched off, determines the value of the bit. Because the an-

tenna circuit of the module and the connected antenna form a resonance circuit with

a specific rise and fall characteristic of the resonance voltage, different RF module

and antenna combinations might need different t_offL and t_offH timing. The values

t_offL and t_offH shown in section 4.3 'Timing Characteristics' are the times applied

to TXCT-. A high Q antenna such as RI-ANT-P02A is used.

Figure 14: Write Pulse Timing for TXCT-

A detailed description of the complete programming sequence is given in the Se-

quence Control Manual (document number 11-06-21-049).

5.5 Antenna Requirements

The antenna for a TIRIS RF module is a coil with the inductance L_ANT and the Q-

factor Q_ANT. To ensure that the antenna can be tuned to resonance with the tuning

capacitors inside the RF Module, the inductance L_ANT for an air coil antenna can

vary in the limits given below:

L_ANT = 115 to 117 µH (at f=134.2 kHz, V=1V)

Q_ANT = 200 or better is recommended for good read/write range.

Some factors which often influence each other, are listed below.

a. The

size

and the

construction

of the antenna coil is a key factor for the generated

magnetic field strength. The larger the area of an air coil antenna or the longer a

ferrite core antenna is, the higher the field strength for a given RFM set-up and a

given Q-factor of the antenna coil.

b. The

quality factor

of the antenna coil is a parameter indicating its efficiency. The

quality depends on the construction and the wire used for the coil. Because of the

high frequency, litze-wire is needed for a high Q-factor. The higher the Q-factor of

the antenna coil the more energy can be “pulled” from the RF module for a given

RF module set-up. If an antenna with ferrite core is used, it must be kept in mind

that it may have a very high quality factor under test conditions, but the quality

factor will drop if a high magnetic field is applied to the ferrite core.

c. A very important factor for a good read/write range is the correct

orientation

polarization

between the transponder antenna and the antenna of the read/write

unit.